This invention relates to a method of calculating the coordinates of a target image where it is displayed on a video monitor, from a composite signal consisting of video signals and synchronizing signals for displaying a target, such as a light-emitter, photographed by a vide camera or a target stored in a video recorder, on the video monitor, and an apparatus for carrying out this method.
For the coordinates of a particular location, a mark, or a target, such as a light-emitter, photographed by a video camera or a target stored in a video recorder where it is displayed on a video monitor, count values of the number of pixel dots are converted into digital values. The coordinates are calculated by the digital values so that these digital coordinates are returned to analog values, which are output to an external device, for example, an image editor.
As mentioned above, when data are processed through means for an analog-to-digital conversion, a digital calculation, and a digital-to-analog conversion, much time is spent until the coordinate values are output. In particular, a video image that has a large number of dots requires an extremely long processing time. In a common video image, images for 60 fields per second are scanned and switched. Unless an arithmetical element has a very high arithmetical processing speed, cases frequently occur in which a timely output of each of the coordinate values is not obtained until one field is completed and the next field appears. Where the coordinate values are calculated and output in succession, output delays may be accumulated to give rise to problems.
It is, therefore, an object of the present invention to provide a method of calculating the coordinates of a target image in which the coordinates of the target image where it is displayed on a monitor can be calculated very rapidly and an apparatus for carrying out this method.
In order to achieve this object, the method of calculating the coordinates of the target image according to the present invention involves measuring time between the generation of a vertical synchronizing signal fetched from a composite signal for displaying the target image on a video monitor and a singular change of a video signal therefrom and calculating the coordinates of the target image displayed on the video monitor from this measured time.
According to this method of calculating the coordinates of a target image, the coordinates of the target image are calculated in accordance with the time between the output of the vertical synchronizing signal and the singular change of the video signal, without requiring the analog-to-digital conversion or digital-to-analog conversion of data. Thus, the data of the coordinates can be obtained in a short processing time.
The method of calculating the coordinates of a target image according to the present invention may be carried out in such a way that Y coordinate is calculated from the time measured and X coordinate is calculated from measuring time between generation of a horizontal synchronizing signal produced immediately before the video signal and the singular change.
Specifically, the video signal bringing about the singular change is a maximum or minimum voltage signal selected from video signals near here.
Such video signal bringing about the singular change may be given from a voltage of a video signal compared with a threshold.
The target image refers to an image of a light-emitter photographed by a video camera.
According to the present invention, an apparatus for calculating the coordinates of a target image to carry out the method of calculating the coordinates of a target image includes a means for generating a composite signal to display a target image on a video monitor, a means for measuring time between the generation of a vertical synchronizing signal fetched from the composite signal and a singular change of a video signal therefrom, and a means for calculating the coordinates of the target image displayed on the video monitor from this measured time.
This apparatus may include a means for calculating Y coordinate of the target image from the time measured above, means for calculating X coordinate from measuring time between the generation of a horizontal synchronizing signal produced immediately before the video signal and the singular change, and means for measuring the time.
This apparatus may have a comparator for selecting a maximum or minimum voltage from video signals near here to extract the video signal bringing about the singular change.
The comparator may be for comparing a voltage of each video signal compared with a threshold.
Also, the means for generating the composite signal is a video camera.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.